1. Field of the Invention
The present invention relates to a piezoelectric energy harvester and a method of manufacturing the same, and more particularly to a piezoelectric energy harvester capable of obtaining sufficient voltage to drive a power conditioning circuit (PCC) without affecting characteristics thereof and a method of manufacturing the same.
2. Discussion of Related Art
Piezoelectric energy harvesters cause a piezoelectric layer to bend, contract, stretch, etc., using vibration, sound waves, ultrasonic waves, etc., thereby generating voltage due to the piezoelectric effect. According to a structure in which a piezoelectric layer is stacked, piezoelectric energy harvesters are classified into various types such as unimorph and bimorph. In general, the bimorph-type piezoelectric energy harvesters in which piezoelectric layers are stacked on the both surfaces of a shim are frequently used.
Voltage generated by such a piezoelectric energy harvester is used to drive an external circuit (a microcontroller unit (MCU), sensor, and radio frequency (RF) transceiver) or a switch of a PCC, which will be described in detail below.
FIGS. 1 and 2 illustrate a conventional piezoelectric energy harvester connected with a PCC and a charger (a electrolytic capacitor, ultra-capacitor or battery).
Referring to FIGS. 1 and 2, when vibration is applied to a conventional piezoelectric energy harvester 100, voltage is generated from piezoelectric layers 130a and 130b formed on both surfaces of a shim 110.
When voltage is generated from the piezoelectric energy harvester 100, a change in voltage is detected by a voltage detector in a PCC 200, and switches S1 and S2 are driven.
However, in these structures, the voltage detector may affect operation of the piezoelectric energy harvester 100 and cause an operating frequency changes, electrical damping, output power loss, etc. It is due to of coupling of mechanics and electronics. Thus, the structures must be designed in consideration of these problems.
To solve these problems, a structure in which a displacement sensor is connected to the exterior of a piezoelectric energy harvester and senses displacement of the piezoelectric energy harvester to drive a switch of a PCC has been suggested.
However, this structure has problems in that a displacement sensor is necessary, the displacement sensor may affect amplitude variation of the piezoelectric energy harvester and cause mechanical damping variation, and the size of the piezoelectric energy harvester increases. Also, when the displacement sensor is contacted with the piezoelectric energy harvester, physical impact may occur on the piezoelectric energy harvester.